1. Field of the Invention
The present invention relates generally to electronic devices with multiple electrical elements and, more particularly, to inductance/capacitance (LC) composite module components having therein a variable capacitor and an inductor.
2. Description of the Prior Art
One prior known LC composite component 1 is shown in FIG. 8. An equivalent electrical circuit of the LC composite component 1 of FIG. 8 is illustrated in FIG. 9. Such LC composite component 1 may be built in radio frequency (RF) modulators for use with video decks, television receivers and the like.
As shown in FIG. 8, the LC composite component 1 consists essentially of a serial combination of a variable capacitor 2 and a coil 3 acting as the inductor. This composite component also includes a first terminal 4 connected to one end of the variable capacitor 2, a second terminal 5 connected to a connection node between the other end of variable capacitor 2 and one end of the coil 3, and a third terminal 6 connected to the other end of coil 3.
As shown in FIG. 8, the LC composite component 1 has an electrically insulating substrate 7. The variable capacitor 2 provided in the LC composite component 1 employs air as the dielectric material thereof, which capacitor includes a rotor 8 and a stator 9 in a way such that the rotor 8 and stator 9 are supported by the substrate 7.
More specifically, the rotor 8 is generally made of a chosen metal and has a rotation shaft section 10 and a plurality of rotor-side electrodes 11 each formed into a semicircular shape, for example, which electrodes are thin plates which are laterally projected from the rotation shaft section 10. Such rotor 8 may typically be structured as an integral cutting-machined element. The rotation shaft section 10 penetrates the substrate 7. On the lower surface side of the substrate 7, a spring washer 12 and fastening or lock ring 13 are engaged on the rotation shaft section 10 for mechanical fixation or caulking of the lower edge part of rotation shaft section 10, thus allowing this shaft section 10 to be rotatably supported on substrate 7.
Additionally, a base 14 of the first terminal 4 is placed between the substrate 7 and spring washer 12, whereby the first terminal 4 is mechanically held with respect to substrate 7, while causing it to be electrically connected to the rotor 8.
Further, an adjustment shaft section 15 made of an electrically insulating material such as resin is engaged with the rotation shaft section 10 at the upper edge portion thereof. The rotation shaft section 10 is formed with a projection 16 for engagement, whereas the adjustment shaft section 15 is formed with an engagement recess 17 engageable with the engagement projection 16, thereby allowing the rotation shaft section 10 and adjustment shaft section 15 to rotate integrally. An adjustment groove 18 engageable with an adjustment hand tool such as a screw driver, for example is formed at the upper edge portion of the adjustment shaft section 15.
The stator 9 has a plurality of thin plate-shaped stator-side electrodes 19 and a spacer 20 inserted between these stator-side electrodes 19. The second terminal 5 is attached so that it penetrates the substrate 7 and further passes through the stator-side electrodes 19 and spacer 20 to be soldered together with these stator-side electrodes 19 and spacer 20, causing these parts to be rigidly mounted with respect to the terminal 5. The stator-side electrodes 19 are placed such that these are insertable into the inner space between the rotor-side electrodes 11 in accordance with rotation of the rotor 8 stated supra.
With the foregoing arrangement, the variable capacitor 2 is achieved. More specifically, the rotor-side electrodes 11 and stator-side electrodes 19 oppose each other with the air acting as the dielectric material, thus forming therebetween an intended electrostatic capacitance, which may be connected between the first and second terminals 4 and 5. Also, by rotating the adjustment shaft section 15 while letting an adjustment hand tool such as a screw driver be engaged with the adjustment groove 18 and then forcing the rotation shaft section 10 to likewise rotate, the rotor 8 is rotated, which changes or modifies the net overlapping or opposite area between the rotor-side electrodes 11 and stator-side electrodes 19, which in turn causes the resulting electrostatic capacitance to vary accordingly.
The coil 3 is of an air-core coil that has its one end soldered to the stator 9 and the other end penetrating the substrate 7 for constituting the third terminal discussed previously. In this way, the LC composite component 1 is obtained wherein the variable capacitor 2 and second terminal 5 are connected to the one end of the coil 3 with the third terminal 6 being coupled to the other end thereof as shown in FIG. 9.
Furthermore, a shield cover 21 is attached to the substrate 7 allowing the variable capacitor 2 and coil 3 to be housed therein. The shield cover 21 has an opening 22 for permitting exposure of the adjustment groove 18 of the adjustment shaft section 15. Upon attachment of the shield cover 21 on substrate 7, the adjustment shaft section 15 comes into engagement with shield cover 21 at the periphery of its opening 22, thus eliminating accidental detachment of it from the rotation shaft section 10.
Unfortunately, the above-mentioned LC composite component 1 presents several problems to be solved in relation to the variable capacitor 2 in particular.
First, since the variable capacitor 2 employs air as its dielectric material, it should be required that the rotor-side electrodes 11 and stator-side electrodes 19 be increased in area in order to obtain an electrostatic capacitance of a desired significance in value, which would result in an increase in the influence of inherent parasitic or stray capacitances therearound.
In addition, such LC composite component 1 is standardized pertinent to its outer size and layout of terminals 4-6, as well as positioning of the adjustment shaft section 15. Accordingly, in cases where the area of rotor-side electrodes 11 is simply expanded in the way discussed supra with the layout location of adjustment shaft section 15 being predefined in particular, it will possibly happen that the device design causes rotor-side electrodes 11 to extrude from the shield cover 21 at a specific rotation position. To avoid this, the shield cover 21 is provided with a window 23 for permitting such extrusion of rotor-side electrodes 11. This would result in a decrease in dust protectability and shield effect provided by the shield cover 21.
Further, the use of a cutting process for obtaining the rotation shaft section 10 with the rotor-side electrodes 11 and employment of a relatively large number of parts for obtaining the structure of stator-side electrodes 19 might negatively impact efforts to reduce cost. This problem will become more serious when the rotor-side electrodes 11 and stator-side electrodes 19 are increased in combination number in order to attain an increased electrostatic capacitance.
Furthermore, where the adjustment shaft 10 is inclined during capacitance adjustment, this causes the distance between the rotor-side electrodes 11 and stator-side electrodes 19 to change, letting the resultant capacitance likewise vary in value, which results in difficulty in achieving the intended adjustment.
Still further, since the rotor-side electrodes 11 and stator-side electrodes 19 are made of a thin plate shape, these elements remain readily vibratable upon application of vibration and mechanical shock thereto, which in turn renders variable the distance between the electrodes 19 and 20, whereby the resulting electrostatic capacitance might vary undesirably.
Yet further, the aforesaid vibration and shock can act to cause the rotor 8 and shield cover 21 to move unintentionally, thus rendering unstable the stray capacitance inherently formed between the rotor 8 and shield cover 21.
Moreover, since the rotor-side electrodes 11 and stator-side electrodes 19 are arranged in such a way that each of them acts as part of a corresponding one of the rotor 8 and stator 9 which are provided at separate locations on the substrate 7, the electrode-to-electrode distance between such rotor-side electrodes 11 and stator-side electrodes 19 remains variable significantly upon application of vibration and/or shock during assembly thereof, which is linked to the risk of unstable electrostatic capacitance. In the worst case, the rotor-side electrodes 11 can be brought into contact with stator-side electrodes 19 raising an electrical short-circuit state.
Additionally, since an electrical connection portion(s) must exist along the electrical conduction path leading from the rotor-side electrodes 11 up to first terminal 4 due to slidable contacts between the base 14 of the terminal 4 and either one of the rotation shaft section 10 and spring washer 12, electrical contact becomes unattainable or unreliable due to corrosion and/or contamination at such slidable contact portions. This would result in loss of intended functions of the variable capacitor 2 and also those of the LC composite component 1.